1. Field of the Invention
The present invention relates to a sheet-shaped switch suitable for use in a keyboard switch or the like, and particularly to a thin sheet-shaped switch.
2. Description of the Related Art
A conventional sheet-like or -shaped switch has been formed thick and at high cost, because first and second insulating sheets on which fixed electrodes and movable electrodes constituting the sheet-shaped switch are respectively printed, and an insulating spacer disposed between the insulating sheets are sufficiently thick.
The conventional sheet-shaped switch will now be described below with reference to FIGS. 8 and 9. A first insulating sheet 1 is formed of an insulating material such as a polyester film. The thickness of the first insulating sheet 1 ranges from about 100 .mu.m to 200 .mu.m, for example. A plurality of fixed electrodes 2 each composed of a conductive material such as a single layer of a mixture of silver and carbon and first electrode patterns 4 each composed of the same material as that for each fixed electrode 2 are formed on the upper surface of the first insulating sheet 1 by printing. The thickness of each of the fixed electrodes 2 and the first electrode patterns 4 ranges from 5 .mu.m to 25 .mu.m.
An insulating spacer 5 is opposed to the first insulating sheet 1 and disposed above the first insulating sheet 1. The insulating spacer 5 has penetrations or through holes which are provided at positions opposed to the fixed electrodes 2 respectively and have sizes which are sufficiently large such that movable electrodes 8 to be described later can be respectively brought into contact with the fixed electrodes 2. Incidentally, the thickness of the insulating spacer 5 ranges from about 100 .mu.m to 200 .mu.m, for example.
A second insulating sheet 7 is composed of an insulating material such as a polyester film. The thickness of the second insulating sheet 7 ranges from about 100 .mu.m to 200 .mu.m, for example. For example, an alphabetical letter or numerical character (not shown) indicative of each switch position is printed on the upper surface of the second insulating sheet 7 or a keytop portion (drive portion) of an unillustrated keyboard switch is disposed on the upper surface thereof. A plurality of movable electrodes 8 each composed of a conductive material such as a single layer of a mixture of silver and carbon, and a plurality of second electrode patterns 10 each composed of the same conductive material as each movable electrode 8 are formed on the lower surface of the second insulating sheet 7 by printing. Incidentally, the thickness of each of the movable electrodes 7 and the second electrode patterns 10 ranges from 5 .mu.m to 25 .mu.m.
The first insulating sheet 1, the insulating spacer 5 and the second insulating sheet 7 are mutually multilayered as shown in FIG. 9. When the electrodes 2 and 8 are disposed so as to be opposed in upward and downward directions within each through hole 6 of the insulating spacer 5 by such a multilayer construction and the electrodes 8 are depressed by the operation of an unillustrated key, the movable electrodes 8 printed on the second insulating sheet 7 are brought into contact with their corresponding fixed electrodes 2. On the other hand, when the depressing force is eliminated, the movable electrodes 8 are restored to their original states by an elastic restoring force of the second insulating sheet 7.
In the sheet-shaped switch having such a structure, a space or interval defined between each fixed electrode 2 and each movable electrode 8 is held by the thickness of the insulating spacer 5 itself. This interval provides a withstand voltage between the fixed electrode 2 and the movable electrode 8. It is therefore necessary to make the insulating spacer 5 thick. Further, when one attempts to increase the withstand voltage, a thicker material is necessary as the insulating spacer 5 correspondingly, whereby a material cost becomes high.
Since the first insulating sheet 1, the insulating spacer 5 and the second insulating sheet 7 respectively use the same material and are formed to the same thickness up to now from the viewpoint of easiness on the fabrication of the sheet-shaped switch, management of the manufacturing process, maintenance, etc., the cost of materials for the sheet-shaped switch becomes high and the sheet-shaped switch is still made thick.